2-5 Percent of Change

Percent of Change

Chapter 2 Lesson 5

What is percent of change????

A percent of change is a ratio that compares the change in quantity to the original amount!

We could have a percent increase (small to big) or a percent decrease (big to small)

Example #1

• Find the percent of change in the cost of gasoline in 1970 ($1.30 per gallon) to 2010 ($2.95 per gallon)

• Step 1: Find the amount of increase

• $2.95 - $1.30 = $1.65

• Step 2: Find the percent increase using the formula then mutliply by 100!

• $1.65/$1.30 = 1.27 --> 127% increase!

Example #2

• The price of a radio was $20. It is on sale for $15. What is the percent of change in the price of a radio.

• Step 1: Find amount of decrease

• $20 - $15 = $5

• Step 2: Find percent of decrease by using the formula and multiply by 100!

• $5/$20 = 0.25 --> 25% decrease!

Multiple Choice

Ella bought a DVD recorder for $280. Now, it is on sale for $220. Find the percent change in the price. Round to the nearest whole percent if necessary!

• 127% decrease

• 27% decrease

• 21% decrease

Percent Error

The percent error is a ratio that compares the inaccuracy of an estimate, or amount of error, to the actual amount.

Percent error is similar to the percent of change, except we just find the amount an estimate is GREATER THAN OR LESS THAN the actual amount.

Example #3

• John wants to practice free-throws. He estimates the distance from the foul line to the hoop and marks it as 13.5 feet. The actual distance should be 15 feet. Find the percent error.

• Step 1: Find the amount of error

• 15 ft - 13.5 ft = 1.5 ft

• Step 2: Find percent error by using the formula and multiply by 100.

• 1.5/15 = 0.1 --> 10% error!

Multiple Choice

Find the percent error if the estimate is $230 and the actual amount is $245. Round to the nearest whole percent.

• 6% error

• 11% error

• 100% error

Multiple Choice

Find the percent of change of going from 30 inches to 24 inches.

• 125% decrease

• 20% decrease

• 80% decrease

Multiple Choice

Find the percent change of $126 to $150

• 84% increase

• 19% increase

• 119% increase

Multiple Choice

Find the percent error: Each week, Mr. Jones goes to the grocery store. Mr. Jones estimates that he will spend $120 when he goes to the store this week. He actually spends $94.

• 78% error

• 128% error

• 28% error